1. Field of the Invention
The invention relates to a baffle plate. More particularly, the invention relates to a baffle plate that is provided between a crankshaft and an oil pan so as to prevent entry of air bubbles into lubricating oil in the oil pan.
2. Description of the Related Art
Generally, lubricating oil is supplied to lubrication portions of a crankshaft, a camshaft, pistons and the like of an internal combustion engine provided in a vehicle such as an automobile. Then, the lubricating oil is stored in an oil pan provided at a bottom portion of the internal combustion engine. The lubricating oil stored in the oil pan is pumped up by an oil pump, filtered and purified by an oil filter, and then, the lubricating oil is supplied to the lubrication portions of the internal combustion engine again.
A baffle plate is installed between the oil pan and the crankshaft. The baffle plate prevents a counter weight of the crankshaft from contacting an oil surface of the lubricating oil in the oil pan. Thus, the baffle plate prevents entry of air bubbles into the lubricating oil in the oil pan due to agitation of the lubricating oil.
Also, the baffle plate suppresses the drive loss of the internal combustion engine by preventing resistance that would be caused by the lubricating oil when rotating the crankshaft if the counter weight had contact with the lubricating oil in the oil pan.
After the lubricating oil is supplied to the lubrication portions of the internal combustion engine, the lubricating oil drops in the cylinder blocks, and the baffle plate receives the lubricating oil. Then, the lubricating oil is discharged (i.e., the lubricating oil drops) into the oil pan from a discharge hole. By buffering the force of the lubricating oil, generation of air bubbles in the surface of the lubricating oil stored in the oil pan is prevented, when the oil is returned to the oil pan.
The lubricating oil to be re-supplied from the oil pan to the lubrication portions of the internal combustion engine is pumped up by the oil pump. Thus, if air bubbles enters the lubricating oil, air remains in a supply passage through which the lubricating oil is supplied from the oil pump to the lubrication portions of the internal combustion engine. Accordingly, the oil pump may not be able to stably supply the lubricating oil to the lubrication portions that need to be lubricated, and a sufficient amount of lubricating oil may not be supplied to the lubrication portions. Thus, it is desirable that no air bubbles should be contained in the lubricating oil stored in the oil pan.
A baffle plate structure described in Japanese Patent Application Publication No. 2007-205228 (JP-A-2007-205228) is known. FIG. 10 shows the baffle plate structure described in the publication. In FIG. 10, a baffle plate 3 is provided between a crankshaft 1 and an oil pan 2. A discharge hole 4 that is open to the oil pan 2 is formed in the baffle plate 3. The discharge hole 4 is located downstream of a perpendicular line A in a rotational direction of the crankshaft 1. The perpendicular line A passes through a rotation center of the crankshaft 1.
Also, a guide groove 5 is formed in the baffle plate 3. The guide groove 5 extends from an upstream side to a downstream side in the rotational direction of the crankshaft 1. A downstream-side end portion of the guide groove 5 in an extending direction, in which the guide grove 5 extends, is positioned lower than a bottom surface 3a of the baffle plate 3.
A counter weight 6 of the crankshaft 1 is located over the guide groove 5. The lubricating oil, which has dropped into the guide groove 5, is brought into the discharge hole 4 along the guide groove 5 by an airflow caused by rotation of the counter weight 6. The counter weight 6 is formed integrally with a crankpin (not shown) of the crankshaft 1, and has a function of maintaining the rotational balance of the crankshaft 1.
Also, in the oil pan 2, a collision wall 7 is provided in a downstream side in the rotational direction of the crankshaft 1. After the lubricating oil flows along the airflow caused by the rotation of the counter weight 6, and is discharged from the discharge hole 4, the lubricating oil collides with the collision wall 7. The collision wall 7 is positioned downstream of the discharge hole 4 in the rotational direction of the crankshaft 1.
After the lubricating oil is used for lubrication and drops onto the baffle plate 3, the lubricating oil flows in the guide groove 5 along the airflow that moves in the rotational direction of the counter weight 6 of the crankshaft 1. Then, the lubricating oil is discharged to the oil pan 2 from the discharge hole 4, and inevitably collides with the collision wall 7 located downstream of the discharge hole 4 in the rotational direction of the crankshaft 1, before dropping onto an oil surface O of the lubricating oil in the oil pan 2.
This avoids the situation where the lubricating oil drops and is discharged directly from the baffle plate 3 onto the oil surface O of the lubricating oil in the oil pan 2. When the lubricating oil collides with the collision wall 7, the vapor-liquid separation of the lubricating oil is accelerated. Then, the lubricating oil flows on the collision wall 7, and is discharged to the oil surface O of the lubricating oil in the oil pan 2. That is, after the vapor-liquid separation of the lubricating oil is accelerated due the collision between the lubricating oil and the collision wall 7, and an amount of air bubbles in the lubricating oil is reduced, the lubricating oil is returned to the oil pan 2.
Accordingly, the lubricating oil in the oil pan 2 is maintained in a state in which a bubble fraction (that is, the proportion of air bubbles in unit volume of the lubricating oil) is small. Thus, the lubricating oil with a small bubble fraction is supplied from the oil pan 2 to the lubrication portions of the internal combustion engine.
However, in the baffle plate structure, since the lubricating oil, which has dropped onto the guide groove 5, is brought along the guide groove 5 to the discharge hole 4 by the airflow caused by the rotation of the counter weight 6, a gap between the counter weight 6 and the guide groove 5 needs to be made small.
However, if the gap between the counter weight 6 and the guide groove 5 is made small, problems described below occur.
If the gap between the counter weight 6 and the guide groove 5 is made small, the lubricating oil flows in an area between the guide groove 5 and the counter weight 6 at a high flow speed due to a Venturi effect associated with the airflow caused by the rotation of the counter weight 6. Since the counter weight 6 is formed integrally with the crankpin of the crankshaft 1, when the counter weight 6 rotates in a direction away from the guide groove 5 due to the rotation of the crankshaft 1, a negative pressure is generated between the counter weight 6 and the guide groove 5 immediately after the counter weight 6 moves away from the guide groove 5. Due to the negative pressure, the lubricating oil in the guide groove 5 is blown together with air, and a large amount of air enters the lubricating oil.
More specifically, since a large amount of air enters the lubricating oil before the lubricating oil is discharged from the discharge hole 4, entry of air into the lubricating oil cannot be prevented in the structure in which the guide groove 5 and the discharge hole 4 are formed in the baffle plate 3. Also, in the baffle plate structure, vapor-liquid separation is performed when the lubricating oil passes through the discharge hole 4, and collides with the collision wall 7 in the oil pan 2. However, since a large amount of air enters the lubricating oil before the lubricating oil is discharged from the discharge hole 4 as described above, the vapor-liquid separation cannot be sufficiently performed only by the collision between the lubricating oil and the collision wall 7. Further, since the collision wall 7 is necessary in addition to the baffle plate 3 in the baffle plate structure, the baffle plate structure is complicated.
In order to prevent entry of air into the lubricating oil due to the Venturi effect, it is conceivable to make the gap between the counter weight 6 and the guide groove 5 large. However, in order to make the gap between the counter weight 6 and the guide groove 5 large, the baffle plate 3 needs to be installed so that that the gap is made large. Accordingly, the height of the engine is made large. Also, since the lubricating oil, which has dropped onto the guide groove 5, needs to be brought along the guide groove 5 to the discharge hole 4 by the airflow caused by the rotation of the counter weight 6, there is a limit in increasing the gap between the counter weight 6 and the guide groove 5.
As a result of making the height of the engine large, an installation space for the engine in an engine room needs to be made large. This makes it difficult to install the engine. Thus, it is desired to prevent entry of air into the lubricating oil using a simple configuration, while making the gap between the counter weight 6 and the guide groove 5 small.